GEO 102 Lecture 25 Outline of Last Lecture I. What is life?Outline of Current Lecture II. Introduction of free oxygenIII. Life and atmosphereIV. What were these organisms?V. stromatolitesCurrent LectureIntroduction to free oxygen- two processes introduced free oxygen into the atmosphereo Hadean/ Archean1. Photochemical dissociation- involves ultraviolet radiation in the upper atmospherea. The radiation disrupts water molecules and releases their oxygen and hydrogenb. This could account for 2% of present-day oxygenc. But with 2% oxygen, ozone forms, creating a barrier against ultraviolet radiation2. More important were the activities of organisms that practiced photosynthesisLife and atmosphere- The first process – making ozone- helped to make later lifeo UV light destroys key building blocks of life- The second process could only occur because of lifeo Irony is that oxygen is deadly to the organisms that produced the oxygenWhat were these organisms?- Single cell (true bacteria)- Not many organelles (simple cells)- Photosynthetic and chemosynthetic - That produced oxygen as a metabolic productFirst fossilsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Photomicrographs from western Australia’s 3.3-to 3.5 billion year old warrawoona groupStromatolites- Present-day stromatolites grow as sediment is trapped on sticky mats of blue-green algae (cyanobacteria) o Now restricted to environments where snails cannot live- The oldest know undisputed stromatolites are found in rocks in South Africao 3.0 billion years old o Probable ones from the Warrowoona Group in Australiao 3.3 to 3.5 billion years
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